A typical emergency response system comprises a telephone connected to a private or public telephone network where the telephone also houses a radio receiver. A person subscribing to this system may wear a portable transmitter, which during an emergency, can be made to transmit coded information to the radio receiver within the telephone. The information is a unique identity code to which that particular phone has been programmed to respond. The telephone then automatically dials a supervising service which provides the identity of the caller and if so equipped establishes a two-way hands-free communication. U.S. Pat. No. 5,337,342 which issued Aug. 9, 1994 to Kruger et al describes such a system.
The automatic dialing can also be initiated by depressing an emergency button on the telephone, but this assumes that the person involved happens to be close to the phone, whereas the use of radio signaling allows the person to activate the system remotely at distances of up to 200 feet.
This system can be used in the home, community living establishments, retirement housing, assistant living buildings, etc. Due to the use of codes many phones can be used within the same facility without mutual interference.
Many facilities which use this type of system are large, comprising several multi-story buildings having common areas such as dining rooms, libraries, games and music rooms etc. As is known, such facilities also typically have long corridors. Further, residents of such facilities tend to be elderly although they may be quite mobile and able to travel freely throughout the premises.
Due to the limited range of the radio communication, which is limited by regulation, and the fact that propagation of radio waves inside a building is damped by walls, floors and ceilings, people may not be able to trigger their own telephone from where they happened to be, and excessive range can also mislead the supervisor as to the true user's location.
In an attempt to solve this problem common receivers (ones which recognize all coded transmissions and hence respond to all system users) can be strategically placed so as to cover the whole facility. The problem occurs that to provide good coverage the reception areas of the receiver will overlap, since radio range is not a precisely determined system parameter. This may misdirect the supervising personnel, for instance tricking them into thinking a caller is in a different building or on a different floor. This may also lead to several calls being activated simultaneously which will unnecessarily occupy the supervising system. The nature of radio propagation is such that it can make it easier to trigger a receiver on the top floor of an adjacent building than to trigger a receiver down a long corridor in the same building and on the same floor as the caller. The problems tend to make simple solutions to the above problem inaccurate and expensive.